Voltage converters are often designed as step-up converters or step-down converters. If a voltage converter is connected on its input side to a battery, whose voltage is larger than a voltage needed by a load, then a step-down conversion is carried out. A step-down converter can also be called a buck-converter.
A typical step-down converter comprises a first switch, a second switch and a coil. A first coil terminal of the coil is coupled via the first switch to a reference potential terminal. The battery is coupled via the second switch to the first coil terminal. A second terminal of the coil is connected to a converter output of the voltage converter. In a first phase, the first switch is in a blocking state and the second switch is in a conducting state providing an input voltage to the coil. Thus, an output voltage can be tapped at the second coil terminal of the coil. In a second phase, the first switch is in a conducting state and the second switch is in a blocking state. In the second phase, current flows from the reference potential terminal via the first switch and the coil to the converter output.
In the first phase, a coil current flowing through the coil increases. Thus, the coil will be charged. In the second phase, the coil current decreases. Thus, the coil will be discharged. A step-down converter may have a limitation in its functionality if a transformation between the input voltage and the output voltage is too large or too small. This especially occurs if the output voltage or a predetermined value of the output voltage is very low. In that case, stability cannot easily be realized.
Document U.S. Pat. No. 8,294,436 B2 relates to a DC/DC converter which is able to perform an up-conversion and a down-conversion.
Data sheet “AS1335-1.5A, 1.5 MHz, Synchronous DC/DC Step-Down Converter”, ams AG, Austria, Revision 1.03 describes a buck converter achieving a minimum output voltage of 0.6 V.
Document US 2009/0273391 A1 refers to a regulated voltage generator.